1. Field of the Invention
The present invention relates to a variable gain RF amplifier, and in particular to a low noise variable gain RF amplifier.
2. Discussion of the Related Art
RF (radio frequency) devices such as radio tuners, mobile telephones, satellite receivers, TV tuners etc. are devices that receive an RF signal. In such devices, input circuitry comprising a low noise amplifier (LNA) is generally provided for amplifying the received RF signal which is for example received via an antenna. The LNA should introduce as little noise as possible to the signal. To avoid unwanted reflections, the input impedance of the LNA is usually matched to the impedance of the antenna. Furthermore, the input circuitry generally includes a variable gain amplifier (VGA) coupled after the LNA, to adjust the amplitude of the RF signal to a range acceptable by downstream circuitry that is to process the RF signal.
A drawback with such RF input circuitry is that in providing a low noise amplifier coupled to a variable gain amplifier, the current consumption is relatively high, and a relatively large amount of area is needed. Furthermore, due to the number of components that are present through which the differential signal must pass, noise may be added to the system.